Drought: What Does the Future Look Like for Farmers and Growers?

The following article summarises the first of three webinars on drought and the changing climate, part of the Growing Kai Under Increasing Dry rolling Symposium held in May 2021, a collaboration between the Deep South, Resilience to Nature's Challenges, and Our Land and Water National Science Challenges.

This webinar discussed changing drought risk, from today through to the end of the century, extreme weather modelling and how science is progressing. Recent extreme weather events were also explored, as were the financial impacts of climate change.

This information forms the basis of guidance and planning at a regional and national level and can give an insight into what the future may look like for farmers and growers in a changing climate.

Andrew Tait

Andrew Tait is NIWA’s Chief Scientist for Climate, Atmosphere and Hazards. He specialises in applications of climate data and products, and climate change impacts and adaptation research.

Climate change projections at all three Representative Concentration Pathways (RCPs) – high, medium and low greenhouse gas concentrations – show that New Zealand will be warmer across the board over the coming decades.

On the high concentration pathway, the average increase by the 2040s will be two degrees compared with pre-industrial records. There will be more precipitation in the west but the east will be drier, and rain will be concentrated within shorter time frames, meaning more dry days are projected.

What does this mean for farmers on the ground?

• Droughty years have become more predominant since 2010 looking at PED (Potential Evapotranspiration Deficit), and a different pattern of drought is expected in the future compared with past observations.
• Drought will begin earlier on average with peaks being more intense, and duration lengthening.
• For the mid-range emissions scenario, farmers in most North Island regions, as well as those in eastern regions of the South Island, especially Canterbury and Eastern Southland, can expect to spend around 10% more time in drought by the middle of this century. Changing evapotranspiration due to increasing temperatures is driving this movement.
• By the mid-late 2000s, almost the entire country except coastal South Island will have exacerbated drought conditions, and this will be even more extreme in the North Island and east of the South Island, particularly during winter.

Ultimately, the emissions pathway we follow in the shorter term will have a significant influence on the temperature profile of New Zealand by the end of the century.

Luke Harrington

Luke Harrington is a Senior Research Fellow at the New Zealand Climate Change Research Institute (Victoria University of Wellington, Te Herenga Waka). Luke's research looks at how climate change is making extreme weather events more likely and/or more intense.

Ozone depletion over Antarctica, together with greenhouse gases affecting storm tracks, mean high-pressure systems are stationing themselves over New Zealand more often, and this impacts our weather.

Luke undertook research on New Zealand’s 2013 drought, which was classed as a severe event due to the high number of dry weather days (caused by sea level pressure). Treasury estimated that it caused loss of around NZ$1.5B.

Luke’s research compared the contemporary climate with that of the late 1800s, in a method known as extreme event attribution. This technique shows to what degree climate change has contributed to an event as compared to how much attribution should be placed with natural weather patterns or random climate variability. Findings suggest that a drought of that intensity was approximately twice as likely to happen in 2013 vs the late 1800s due to climate change.

How can research inform farmers on the ground?

There might be a doubling in drought frequency with every degree of global warming, but extreme hot days will likely increase five-,10- or 20-fold per degree of warming.

This is important because the biggest impact of drought may be in animal heat stress, which in turn may cause a decline in milk yields.

Sue Rosier

Dr Suzanne Rosier is a climate scientist at NIWA in Wellington. She played a key part in helping launch weather@home ANZ to the public, and has subsequently analysed its large New Zealand datasets with a particular focus on extreme rainfall.

When investigating weather extremes, complex models can be of limited use as they are very expensive and computationally heavy to run, meaning other instruments are needed.

One useful resource is Weather@Home, an Oxford-based tool containing an Australia/New Zealand model which itself has a regionally specific model embedded within it. The initiative runs on volunteers’ computers throughout the world.

The model provides grid information down to 50km2, which is not the finest scale available, however, there is an inverse relationship between detail and accuracy. At this moderate scale, researchers can have higher confidence in the distribution’s tails for temperature and precipitation, for example, especially for rare climatic extremes.

This model suggests 1.5 – 2 degrees warming (based on the Paris agreement) compared with pre-industrial temperatures, and there is also a +3 degree future run as well. This tool has been used for some Treasury work on extreme weather impacts and costs of climate change.

More information:

• Growing Kai Under Increasing Dry report
• Webinar videos and summaries, and symposium panel discussion summaries can be found at ourlandandwater.weaveclient.site/kaiunderdry

Further resources (Andrew Tait):

• Our Future Climate NZ contains maps and charts of climate change projections across NZ
• NZ Drought Index (NZDI)
• Full report

Further resources (Luke Harrington):

• Research looking climate change preparedness includes research from Deep South and Our Land and Water's Land Use Opportunities programme.
• Harrington, L. J. et al, 2016: Investigating event-specific drought attribution using self-organizing maps. Journal of Geophysical Research: Atmospheres, 121, doi: 10.1002/2016JD025602.
• Harrington, L. J., 2021: Rethinking extreme heat in a cool climate: A New Zealand case study. Environmental Research Letters. 16 (3), 034030. doi: 10.1088/1748-9326/abbd61

Further resources (Sue Rosier):

• https://deepsouthchallenge.co.nz/research-project/future-extreme-weather-in-aotearoa/
• https://deepsouthchallenge.co.nz/resource/the-economic-costs-of-hurricane-harvey-attributable-to-climate-change/
• https://link.springer.com/article/10.1007/s10584-020-02692-8